Laser light source

A laser light source is disclosed consisting of first and second lasers that respectively generate laser beams of wavelengths λ1 and λ2. Wavelength λ1 is in the range of 0.9-1.0 μm. A nonlinear optical crystal uses the laser beams of wavelengths λ1 and λ2 as inputs, and outputs a coherent beam having a wavelength λ3 of a difference frequency that satisfies a relationship of 1/λ1−1/λ2=1/λ3. The nonlinear optical crystal has a periodically poled structure of a single period. The wavelength λ3 of the difference frequency varies between 3.1 μm and 2.0 μm when the wavelength λ2 varies between 1.3 μm and 1.8 μm.